Control system for a furfural refining unit receiving heavy sweet charge oil

ABSTRACT

A furfural refining unit treats heavy sweet charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a flash point temperature analyzer, a sulfur analyzer and viscosity analyzers; all analyzing the heavy sweet charge oil and providing corresponding signals, sensors sense the flow rates of the charge oil and the solvent flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the heavy sweet charge oil and the furfural flow rates is controlled in accordance with the signals from all the analyzers and all the sensors, while the other flow rate of the heavy sweet charge oil and the furfural flow rates is constant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation as to all subject matter common to U.S. application Ser. No. 851,912 filed Nov. 16, 1977 now abandoned by Avilino Sequeira, Jr., John D. Begnaud and Frank. L. Barger, and assigned to Texaco Inc., assignee of the present invention, and a continuation-in-part for additional subject matter.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to control systems and methods in general and, more particularly, to control systems and methods for oil refining units.

SUMMARY OF THE INVENTION

A furfural refining unit treats heavy sweet charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a flash point temperature analyzer, a sulfur analyzer and viscosity analyzers. The analyzers analyze the heavy sweet charge oil and provide corresponding signals. Sensors sense the flow rates of the charge oil and the furfural flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. The flow rate of the heavy sweet charge oil of the furfural is controlled in accordance with the signals provided by all the sensors and the analyzers while the other flow rate of the heavy sweet charge oil and the furfural flow rates is constant.

The objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a furfural refining unit in partial schematic form and a control system, constructed in accordance with the present invention, in simple block diagram form.

FIG. 2 is a detailed block diagram of the control means shown in FIG. 1.

FIGS. 3 through 14 are detailed block diagrams of the H computer, the K signal means, the H signal means, the KV computer, the VI signal means, the SUS computer, the SUS₂₁₀ computer, the W computer, the VI_(DWCO) computer, the VI_(DWCP) computer, the A computer and the J computer, respectively, shown in FIG. 2.

DESCRIPTION OF THE INVENTION

An extractor 1 in a furfural refining unit is receiving heavy sweet charge oil by way of a line 4 and furfural solvent by way of a line 7 and providing raffinate to recovery by way of a line 10, and an extract mix to recovery by way of a line 14.

Heavy sweet charge oil is a charge oil having a sulfur content less than a predetermined sulfur content and having a kinematic viscosity, corrected to a predetermined temperature, greater than a predetermined kinematic viscosity. Preferably, the predetermined sulfur content is 1.0%, the predetermined temperature is 210° F., and the predetermined kinematic viscosity is 15.0, respectively. The temperature in extractor 1 is controlled by cooling water passing through a line 16. A gravity analyzer 20, flash point analyzer 22 and viscosity analyzers 23 and 24, and a sulfur analyzer 28 sample the charge oil in line 4 and provide signals API, FL, KV₂₁₀, KV₁₅₀ and S, respectively, corresponding to the API gravity, the flash point, the kinematic viscosity at 210° F. & 150° F., and sulfur content, respectively.

A flow transmitter 30 in line 4 provides a signal CHG corresponding to the flow rate of the charge oil in line 4. Another flow transmitter 33 in line 7 provides a signal SOLV corresponding to the furfural flow rate. A temperature sensor 38, sensing the temperature of the extract mix leaving extractor 1, provides a signal T corresponding to the sensed temperature. All signals hereinbefore mentioned are provided to control means 40.

Control means 40 provides signal C to a flow recorder controller 43. Recorder controller 43 receives signals CHG and C and provides a signal to a valve 48 to control the flow rate of the charge oil in line 4 in accordance with signals CHG and C so that the charge oil assumes a desired flow rate. Signal T is also provided to temperature controller 50. Temperature controller 50 provides a signal to a valve 51 to control the amount of cooling water entering extractor 1 and hence the temperature of the extract-mix in accordance with its set point position and signal T.

The following equations are used in practicing the present invention for heavy sweet charge oil:

    H.sub.210 =1n1n(KV.sub.210 +C.sub.1)                       (1)

where H₂₁₀ is a viscosity H value for 210° F., KV₂₁₀ is the kinematic viscosity of the charge oil at 210° F. and C₁ is a constant having a preferred value of 0.6.

    H.sub.150 =1n1n(KV.sub.150 +C.sub.1)                       (2)

where H₁₅₀ is a viscosity H value for 150° F., and KV₁₅₀ is the kinematic viscosity of the charge oil at 150° F.

    K.sub.150 =[C.sub.2 -1n(T.sub.150 +C.sub.3 ]/C.sub.4       (3)

where K₁₅₀ is a constant needed for estimation of the kinematic viscosity at 100° F., T₁₅₀ is 150, and C₂ through C₄ are constants having preferred values of 6.5073, 460 and 0.17937, respectively.

    H.sub.100 =H.sub.210 +(H.sub.150 --H.sub.210)/K.sub.150    (4)

where H₁₀₀ is a viscosity H value for 100° F.

    KV.sub.100 =exp[exp(H.sub.100)]--C.sub.1                   (5)

where KV₁₀₀ is the kinematic viscosity of the charge oil at 100° F. ##EQU1## where SUS is the viscosity in Saybolt Universal Seconds and C₅ through C₁₂ are constants having preferred values of 4.6324, 1.0, 0.03264, 3930.2, 262.7, 23.97, 1.646 and 10⁻⁵, respectively.

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS  (7)

where SUS₂₁₀ is the viscosity in Saybolt Universal Seconds at 210° F. and C₁₃ through C₁₆ are constants having preferred values of 1.0, 0.000061, 210 and 100, respectively. ##EQU2## where W is the percent wax in the charge oil, and C₄₃ through C₄₉ are constants having preferred values of 51.17 4.3135, 182.83, 5.2388, 0.101, 6.6106 and 0.19609, respectively. ##EQU3## where C₆₇ through C₇₃ are constants having preferred values of 168.538, 0.0468, 3.63863, 0.17523, 0.41542, 0.00106 and 0.21918, respectively.

    VI.sub.DWCP =VI.sub.DWCO +(Pour) [C.sub.21 -C.sub.22 1nSUS.sub.210 +C.sub.23 (1nSUS.sub.210).sup.2 ]                         (10)

where VI_(DWCP) and Pour are the viscosity index of the dewaxed charge at a predetermined temperature and the Pour Point of the dewaxed product, respectively, and C₂₁ through C₂₃ are constants having preferred values of 2.856, 1.18 and 0.126, respectively.

    ΔVI=VI.sub.RO -VI.sub.DWCO =VI.sub.RP -VI.sub.DWCP   (11)

where VI_(RO) and VI_(RP) are the VI of the refined oil at 0° F., and the predetermined temperature, respectively. ##EQU4## where C₇₄ through C₇₉ are constants having preferred values of 503.518, 0.04423, 54.58305, 0.00055, 0.03745 and 1.38869.

    J=(ΔVI-C.sub.80 -C.sub.81 √T)/[-C.sub.82 T+C.sub.83 (A)(T)], (13)

where J is the furfural dosage and C₈₀ through C₈₃ are constants having preferred values of 10.272, 1.0194, 0.00067611 and 0.000004029, respectively.

    C=(SOLV) (100)/J                                           (14)

where C is the new charge oil flow rate.

Referring now to FIG. 2, signal KV₂₁₀ is provided to an H computer 50 in control means 40, while signal KV₁₅₀ is applied to an H computer 50A. It should be noted that elements having a number and a letter suffix are similar in construction and operation as to those elements having the same numeric designation without a suffix. All elements in FIG. 2, except elements whose operation is obvious, will be disclosed in detail hereinafter. Computers 50 and 50A provide signals E₁ and E₂ corresponding to H₂₁₀ and H₁₅₀, respectively, in equations 1 and 2, respectively, to H signal means 53. K signal means 55 provides a signal E₃ corresponding to the term K₁₅₀ in equation 3 to H signal means 53. H signal means 53 provides a signal E₄ corresponding to the term H₁₀₀ in equation 4 to a KV computer 60 which provides a signal E₅ corresponding to the term KV₁₀₀ in accordance with signal E₄ and equation 5 as hereinafter explained.

Signals E₅ and KV₂₁₀ are applied to VI signal means 63 which provides a signal E₆ corresponding to the viscosity index.

An SUS computer 65 receives signal KV₂₁₀ and provides a signal E₇ corresponding to the term SUS in accordance with the received signals and equation 6 as hereinafter explained.

An SUS 210 computer 68 receives signal E₇ and applies signal E₈ corresponding to the term SUS₂₁₀ in accordance with the received signal and equation 7 as hereinafter explained.

A W computer 69 receives signals KV₂₁₀, S and API and provides a signal E₉ corresponding to the term W in equation 8 in accordance with the received signals and equation 8 as hereinafter explained.

A VI_(DWCO) computer 70 receives signal RI, E₉, API, FL and E₆ and provides a signal E₁₀ corresponding to the term VI_(DWCO) in accordance with the received signals and equation 9 as hereinafter explained.

A VI_(DWCP) computer 72 receives a signal E₈ and E₁₀ and provides a signal E₁₁ corresponding to the term VI_(DWCP) in accordance with the received signals and equation 10. Subtracting means 76 performs the function of equation 11 by subtracting signal E₁₁ from a direct current voltage V₉, corresponding to the term VI_(RP), to provide a signal E₁₂ corresponding to the term ΔVI in equation 11.

An A computer 79 receives signals KV₂₁₀, API,S and FL and provides a signal A corresponding to the term A in equation 12, in accordance with the received signals and equation 12 as hereinafter explained.

A J computer 80 receives signals T, A and E₂ and provide a signal E₁₃ corresponding to the term J in accordance with the received signals and equation 13 as hereinafter explained to a divider 83.

Signal SOLV is provided to a multiplier 82 where it is multiplied by a direct current voltage V₂ corresponding to a value of 100 to provide a signal corresponding to the term (SOLV) (100) in equation 14. The product signal is applied to divider 83 where it is divided by signal E₁₃ to provide signal C corresponding to the desired new charge oil flow rate.

It would be obvious to one skilled in the art that if the charge oil flow rate was maintained constant and the furfural flow rate varied, equation 14 would be rewritten as

    SO=(J) (CHG)/100                                           (15)

where SO is the new furfural flow rate. Control means 40 would be modified accordingly.

Referring now to FIG. 3, H computer 50 includes summing means 112 receiving signal KV₂₁₀ and summing it with a direct current voltage C₁ to provide a signal corresponding to the term [KV₂₁₀ +C₁ ] shown in equation 1. The signal from summing means 112 is applied to a natural logarithm function generator 113 which provides a signal corresponding to the natural log of the sum signal which is then applied to another natural log function generator 113A which in turn provides signal E₁₀.

Referring now to FIG. 4, K signal means 55 includes summing means 114 summing direct current voltages T₁₅₀ and C₃ to provide a signal corresponding to the term [T₁₅₀ +C₃ ] which is provided to a natural log function generator 113B which in turn provides a signal corresponding to the natural log of the sum signal from summing means 114. Subtracting means 115 subtracts the signal provided by function generator 113B from a direct current voltage C₂ to provide a signal corresponding to the numerator of equation 3. A divider 116 divides the signal from subtracting means 115 with a direct current voltage C₄ to provide signal E₃.

Referring now to FIG. 5, H signal means 53 includes subtracting means 117 which subtracts signal E₁ from signal E₂ to provide a signal corresponding to the term H₁₅₀ -H₂₁₀, in equation 4, to a divider 118. Divider 118 divides the signal from subtracting means 117 by signal E₃. Divider 114 provides a signal which is summed with signal E₁ by summing means 119 to provide signal E₄ corresponding to H₁₀₀.

Referring now to FIG. 6, a direct current voltage V₃ is applied to a logarithmic amplifier 120 in KV computer 60. Direct current voltage V₃ corresponds to the mathematical constant e. The output from amplifier 120 is applied to a multiplier 122 where it is multiplied with signal E₄. The product signal from multiplier 122 is applied to an antilog circuit 125 which provides a signal corresponding to the term exp (H₁₀₀) in equation 5. The signal from circuit 125 is multiplied with the output from logarithmic amplifier 120 by a multiplier 127 which provides a signal to antilog circuit 125A. Circuit 125A is provided to subtracting means 128 which subtracts a direct current voltage C₁ from the signal from circuit 125A to provide signal E₅.

Referring now to FIG. 7, VI signal means 63 is essentially memory means which is addressed by signals E₅, corresponding to KV₁₀₀, and signal KV₂₁₀. In this regard, a comparator 130 and comparator 130A represent a plurality of comparators which receive signal E₅ and compare signal E₅ to reference voltages, represented by voltages R₁ and R₂, so as to decode signal E₅. Similarly, comparators 130B and 130C represent a plurality of comparators receiving signal KV₂₁₀ which compare signal KV₂₁₀ with reference voltages RA and RB so as to decode signal KV₂₁₀. The outputs from comparators 130 and 130B are applied to an AND gate 133 whose output controls a switch 135. Thus, should comparators 130 and 130B provide a high output, AND gate 133 is enabled and causes switch 135 to be rendered conductive to pass a direct current voltage V_(A) corresponding to a predetermined value, as signal E₆ which corresponds to VI. Similarly, the outputs of comparators 130 and 130C control an AND gate 133A which in turn controls a switch 135A to pass or to block a direct current voltage V_(B). Similarly, another AND gate 133B is controlled by the outputs from comparators 130A and 130B to control a switch 135B so as to pass or block a direct current voltage V_(C). Again, an AND gate 133C is controlled by the outputs from comparators 130A and 130C to control a switch 135C to pass or to block a direct current voltage V_(D). The outputs of switches 135 through 135C are tied together so as to provide a common output.

Referring now to FIG. 8, the SUS computer 65 includes multipliers 136, 137 and 138 multiplying signal KV₂₁₀ with direct current voltages C₉, C₇ and C₅, respectively, to provide signals corresponding to the terms C₉ (KV₂₁₀), C₇ (KV₂₁₀) and C₅ (KV₂₁₀), respectively in equation 6. A multiplier 138 effectively squares signal KV₂₁₀ to provide a signal to multipliers 140, 141. Multiplier 140 multiplies the signal from multiplier 139 with a direct current voltage C₁₀ to provide a signal corresponding to the term C₁₀ (KV₂₁₀)² in equation 6. Multiplier 141 multiplies the signal from multiplier 139 with signal KV₂₁₀ to provide a signal corresponding to (KV₂₁₀)³. A multiplier 142 multiplies the signal from multiplier 141 with a direct current voltage C₁₁ to provide a signal corresponding to the term C₁₁ (KV₂₁₀)³ in equation 6. Summing means 143 sums the signals from multipliers 136, 140 and 142 with a direct current voltage C₈ to provide a signal to a multiplier 144 where it is multiplied with a direct current voltage C₁₂. The signal from multiplier 137 is summed with a direct current voltage C₆ by summing means 145 to provide a signal corresponding to the term [C₆ +C₇ (KV₂₁₀ ]. A divider 146 divide the signal provided by summing means 145 with the signal provided by multiplier 144 to provide a signal which is summed with the signal from multiplier 138 by summing means 147 to provide signal E₇.

Referring now to FIG. 9, SUS₂₁₀ computer 68 includes subtracting means 148 which subtracts a direct current voltage C₁₆ from another direct current voltage C₁₆ from another direct current voltage C₁₅ to provide a signal corresponding to the term (C₁₅ -C₁₆) in equation 7. The signal from subtracting means 148 is multiplied with a direct current voltage C₁₄ by a multiplier 149 to provide a product signal which is summed with another direct current voltage C₁₃ by summing means 150. Summing means 150 provides a signal corresponding to the term [C₁₃ +C₁₄ (C₁₅ -C₁₆ ] in equation 7. The signal from summing means 150 is multiplied with signal E₇ by a multiplier 152 to provide signal E₈.

Referring now to FIG. 10, there is shown W computer 69 having multipliers 155, 156 and 157 receiving signal API. Multiplier 155 multiplies signal API with signal S to provide a product signal to another multiplier 160 where it is multiplied with a direct current voltage C₄₉ to provide a signal corresponding to the term C₄₉ (S) (API) in equation 8. Multiplier 156 effectively squares signal API and provides a signal to another multiplier 163 where it is multiplied with a direct current voltage C₄₇ to provide a signal corresponding to the term (C₄₇) (API)². Multiplier 157 multiplies signal API with a direct current voltage C₄₄ to provide a signal corresponding to the term C₄₄ (API). A divider 166 divides signal API with signal KV₂₁₀ to provide another signal to a multiplier 168 where it is multiplied with a direct current voltage C₄₈ which in turn provides a signal corresponding to the term [C₄₈ (API)/(KV₂₁₀)] in equation 8. A divider 170 divides a direct current voltage C₄₅ with signal KV₂₁₀ to provide a signal corresponding to the term C₄₅ /(KV₂₁₀). A multiplier 173 multiplies signal S with a direct current voltage C₄₆. Summing means 175 sums a direct current voltage C₄₃ with the signals provided by multipliers 160, 163 and divider 170. Other summing means 176 sums the signals provided by multipliers 157, 168 and 173. Subtracting means 179 subtracts the signal provided by summing means 176 from the signal provided by summing means 175 to provide signal E₉.

Referring now to FIG. 11, VI_(DWCO) computer 70 includes a multiplier 180 which effectively squares signal KV₂₁₀ and provides it to a multiplier 181 where it is multiplied direct current voltage C₆₈. Multiplier 181 provides a signal corresponding to the term C₆₈ (KV₂₁₀)² in equation 9. A multiplier 182 multiplies signals KV₂₁₀, E₉ to provide a signal to another multiplier 183 where it is multiplied with direct current voltage C₇₃. Multiplier 183 provides a signal corresponding to the term C₇₃ (W) (KV₂₁₀) in equation 9. A multiplier 184 multiplies signal E₆ with a direct current voltage C₆₉ to provide a signal corresponding to the term C₆₉ (VI) in equation 9. Another multiplier 185 multiplies signals E₆, FL to provide a signal to a multiplier 186 where it is multiplied with a direct current voltage C₇₂. Multiplier 186 provides a signal corresponding to the term C₇₂ (FL) (VI) in equation 9. A multiplier 188 multiplies signals E₆, API to provide a signal to another multiplier 189 where it is multiplied with direct current voltage C₇₀. Product signals provided by multipliers 183, 189 are summed with another direct current voltage C₆₇ by summing means 192 to provide a signal corresponding to the term -C₆₇ -C₇₀ (API) (VI)-C₇₃ (W) (KV₂₁₀). A multiplier 193 effectively squares signal API and provides it to a multiplier 194 where it is multiplied with a direct current voltage C₇₁. Multiplier 194 provides a signal corresponding to the term C₇₁ (API)² in equation 9. Summing means 197 sums the signal from multipliers 181, 184, 186 and 196. Subtracting means 199 subtracts the signal provided by summing means 192 from the signal provided by summing means 197 to provide signal E₁₀.

VI_(DWCP) computer 72 shown in FIG. 12, includes a natural logarithm function generator 200 receiving signal E₈ and providing a signal corresponding to the term 1nSUS₂₁₀ to multipliers 201 and 202. Multiplier 201 multiplies the signal from function generator 200 with a direct current voltage C₂₂ to provide a signal corresponding to the term C₂₂ 1n SUS₂₁₀ in equation 10. Multiplier 202 effectively squares the signal from function generator 200 to provide a signal that is multiplied with the direct current voltage C₂₃ by a multiplier 205. Multiplier 205 provides a signal corresponding to the term C₂₃ (1n SUS₂₁₀)² in equation 10. Subtracting means 206 subtracts the signals provided by multiplier 201 from the signal provided by multiplier 205. Summing means 207 sums the signal from subtracting means 206 with a direct current voltage C₂₁. A multiplier 208 multiplies the sum signals from summing means 207 with a direct current voltage POUR to provide a signal which is summed with signal E₉ by summing means 210 which provides signal E₁₁.

FIG. 13 shows A computer 78 having a multiplier 215 effectively squaring signal KV₂₁₀ to provide a signal which is multiplied with a direct current voltage C₇₅ by a multiplier 216 which provides a signal corresponding to the term C₇₅ (KV₂₁₀)² in equation 12. Multiplier 218 multiplies signals KV₂₁₀, S to provide a signal that is multiplied with a direct current voltage C₇₉ by a multiplier 220. Multiplier 220 provides a signal corresponding to the term C₇₉ (KV₂₁₀) (S) in equation 12. A multiplier 223 multiplies signals API, FL to provide a signal to another multiplier 224 where it multiplies a direct current voltage C₇₈. Multiplier 224 provides a signal corresponding to the term C₇₈ (FL) (API) in equation 12. Summing means 226 essentially sums all of the negative terms in equation 12 by summing the signals from multipliers 216, 220 and 224. A multiplier 229 multiplies signal S with a direct current voltage C₇₆ to provide a signal corresponding to the term C₇₆ (S) in equation 12. Another multiplier 230 effectively squares signal FL and provides it to yet another multiplier 231 where it is multiplied with a direct current voltage C₇₇. Multiplier 231 provides a signal corresponding to the term C₇₇ (FL)². Summing means 235 essentially sums the positive terms of equation 12 by summing a direct current voltage C₇₄ with the signals provided by multipliers 229 and 231. Subtracting means 237 subtracts the signal provided by summing means 236 from the signal provided by summing means 235 to provide signal A.

Referring now to FIG. 14, J computer 80 includes a square root circuit 240 receiving signal T and providing a signal to a multiplier 241 where it is multiplied with a direct current voltage C₈₁ to provide a signal to subtracting means 242. Subtracting means 242 subtracts a signal provided by multiplier 241 from signal E₁₂ to provide a signal corresponding to the term ΔVI-C₈₁ √T in equation 13. Subtracting means 242 provides a signal to another subtracting means 243 which subtracts a direct current voltage C₈₀ to provide a signal corresponding to the term (ΔVI-C₈₀ -C₈₁ √T) in equation 13. A multiplier 246 multiplies signal T with a direct current voltage C₈₂ to provide a signal corresponding to the term C₈₂ T in equation 13. Another multiplier 250 multiplies signal T with signal A to provide a signal to another multiplier 252 where it is multiplied with a direct current voltage C₈₃. Multiplier 252 provides a signal corresponding to the term C₈₃ (A) (T) in equation 13. Subtracting means 255 subtracts the product signal from multiplier 246 from the signal provided by multiplier 252 to provide a signal which is divided into the signal provided by subtracting means 243 by a divider 257. Divider 257 provides signal E₁₃.

The present invention as hereinbefore described controls a furfural refining unit receiving heavy sweet charge oil to achieve a desired charge oil flow rate for a constant furfural flow rate. It is also within the scope of the present invention, as hereinbefore described, to control the furfural flow rate while the heavy sweet charge oil flow is maintained at a constant rate. 

What is claimed is:
 1. A control system for a furfural refining unit receiving heavy sweet charge oil and furfural solvent, one of which is maintained at a fixed rate while the flow rate of the other is controlled by the control system, wherein the system treats the received heavy sweet charge oil with the received furfural to yield extract mix and raffinate, comprising gravity analyzer means for sampling the heavy sweet charge oil and providing a signal API corresponding to the API gravity of the heavy sweet charge oil, flash point analyzer means for sampling the heavy sweet charge oil and providing a signal FL corresponding to the flash point temperature of the heavy sweet charge oil, viscosity analyzer means for sampling the heavy sweet charge oil and providing signals KV₁₅₀ and KV₂₁₀ corresponding to the kinematic viscosities, corrected to 150° F. and 210° F., respectively, sulfur analyzer means for sampling the heavy sweet charge oil and providing a signal S corresponding to the sulfur content of the heavy sweet charge oil, flow rate sensing means for sensing the flow rates of the heavy sweet charge oil and of the furfural and providing signals CHG and SOLV, corresponding to the charge oil flow rate and the furfural flow rate, respectively, temperature sensing means sensing the temperature of the extract mix and providing a corresponding signal T, and control means connected to all of the analyzer means, and to all the sensing means for controlling the other flow rate of the heavy sweet charge oil and the furfural flow rates in accordance with signals API, FL, KV₁₅₀, KV₂₁₀, S, T, CHG and SOLV; wherein said control means includes VI signal means connected to the viscosity analyzer means for providing a signal VI corresponding to the viscosity index of the heavy sweet charge oil in accordance with the kinematic viscosity signals KV₁₅₀ and KV₂₁₀ ; SUS₂₁₀ signal means connected to the viscosity analyzer means for providing a signal SUS₂₁₀ corresponding to the heavy sweet charge oil viscosity in Saybolt Universal Seconds corrected to 210° F.; W signal means connected to the viscosity analyzer means, to the gravity analyzer means and to the sulfur analyzer means for providing a signal W corresponding to the wax content of the heavy sweet charge oil in accordance with signals KV₂₁₀, API and S; A signal means connected to the gravity analyzer means, to the viscosity analyzer means, to the sulfur analyzer means, to the flash point temperature analyzer means and to the VI signal means for providing a signal A corresponding to an interim factor A in accordance with signals KV₂₁₀, S, API, VI and FL; ΔVI signal means connected to the viscosity analyzer means, to the gravity analyzer means, to the flash point temperature analyzer means, to the VI signal means, the W signal means and the SUS₂₁₀ signal means and receiving a DC voltage VI.sub. RP for providing a signal ΔVI corresponding to the change in viscosity index in accordance with signals KV₂₁₀, API, VI, FL, W and SUS₂₁₀ and voltage VI_(RP) ; J signal means receiving direct current voltages C₈₀ through C₈₃ and being connected to ΔVI signal means, to the A signal means, to the temperature sensing means for providing a J signal corresponding to a furfural dosage for heavy sweet charge oil in accordance with the ΔVI signal, signals A and T, voltages C₈₀ through C₈₃ and the following equation:

    J=(ΔVI-C.sub.80 -C.sub.81 √T)/[-C.sub.82 T+C.sub.83 (A)(T)],

where C₈₀ through C₈₃ are constants; control signal means connected to the J signal means and to the flow rate sensing means for providing a control signal in accordance with the J signal and one of the sensed flow rate signals, and apparatus means connected to the control signal means for controlling the one flow rate of the heavy sweet charge oil and furfural flow rates in accordance with the control signal.
 2. A system as described in claim 1 in which the SUS₂₁₀ signal means includes SUS signal means connected to the viscosity analyzer means, and receiving direct current voltages C₅ through C₁₂ for providing a signal SUS corresponding to an interim factor SUS in accordance with signal KV₂₁₀, voltages C₅ through C₁₂ and the following equation: ##EQU5## where C₅ through C₁₂ are constants; and SUS₂₁₀ network means connected to the SUS signal means and to the ΔVI signal means and receiving direct current voltages C₁₃ through C₁₆ for providing signal SUS₂₁₀ to the ΔVI signal means in accordance with signal SUS, voltages C₁₃ through C₁₆ and the following equation:

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS,

where C₁₃ through C₁₆ are constants.
 3. A system as described in claim 2 in which the W signal means further receives direct current voltages C₄₃ through C₄₉ and provides signal W in accordance with signals API, KV₂₁₀ and S, voltages C₄₃ through C₄₉, and the following equation: ##EQU6## where C₄₃ through C₄₉ are constants.
 4. A system as described in claim 3 in which the VI signal means includes K signal means receiving direct current voltages C₂, C₃, C₄ and T₁₅₀ for providing a signal K₁₅₀ corresponding to the kinetic viscosity of the charge oil corrected to 150° F. in accordance with voltages C₂, C₃, C₄ and T₁₅₀, and the following equation:

    K.sub.150 =[C.sub.2 -1n(T.sub.150 +C.sub.3)]/C.sub.4,

where C₂ through C₄ are constants, and T₁₅₀ corresponds to a temperature of 150° F.; H₁₅₀ signal means connected to the viscosity analyzer means and receiving a direct current voltage C₁ for providing a signal H₁₅₀ corresponding to a viscosity H value for 150° F. in accordance with signal KV₁₅₀ and voltage C₁ and the following equation:

    H.sub.150 =1n1n(KV.sub.150 +C.sub.1),

where C₁ is a constant; H₁₂₀ signal means connected to the viscosity analyzer means and receiving voltage C₁ for providing signal H₂₁₀ corresponding to a viscosity H value for 210° F. in accordance with signal KV₂₁₀, voltage C₁ and the following equation:

    H.sub.210 =1n1n(KV.sub.210 +C.sub.1),

H₁₀₀ signal means connected to the K signal means, to the H₁₅₀ signal means and the H₂₁₀ signal means for providing a signal H₁₀₀ corresponding to a viscosity H value for 100° F., in accordance with signals H₁₅₀, H₂₁₀ and K₁₅₀ and the following equation:

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150,

KV₁₀₀ signal means connected to the H₁₀₀ signal means and receiving voltage C₁ for providing a signal KV₁₀₀ corresponding to a kinetic viscosity for the charge oil corrected to 100° F. in accordance with signal H₁₀₀, voltage C₁, and the following equation:

    KV.sub.100 =exp[exp(H.sub.100)]-C.sub.1,

and VI memory means connected to the KV₁₀₀ signal means and to the viscosity analyzer means having a plurality of signals stored therein, corresponding to different viscosity index and controlled by signals KV₁₀₀ and KV₂₁₀ to select a stored signal and providing the selected stored signal as signal VI.
 5. A system as described in claim 4 in which the A signal means also receives direct current voltages C₇₄ through C₇₉ and provides signal A in accordance with signals KV₂₁₀, S, FL, and API, voltages C₇₄ through C₇₉, and the following equation: ##EQU7## where C₇₄ through C₇₉ are constants.
 6. A system as described in claim 5 in which the ΔVI signal means includes VI_(DWCO) signal means connected to the viscosity analyzer means, to the gravity analyzer means, to the flash point temperature analyzer means, to the VI signal means, to the W signal means and receiving direct current voltages C₆₇ through C₇₃ for providing a signal VI_(DWCO) in accordance with signals KV₂₁₀, VI, API, FL and W, voltages C₆₇ through C₇₃, and the following equation: ##EQU8## where C₆₇ through C₇₃ are constants; a VI_(DWCP) signal means connected to the VI_(DWCO) signal means and to the SUS₂₁₀ signal means, and receiving direct current voltages C₂₁ through C₂₃ and Pour, for providing a signal VI_(DWCP) in accordance with signals VI_(DWCO) and SUS₂₁₀, voltages C₂₁ through C₂₃, and Pour, and the following equation:

    VI.sub.DWCP =VI.sub.DWCO +(POUR)[C.sub.21 -C.sub.22 1nSUS.sub.210 +C.sub.23 (1nSUS.sub.210).sup.2 ],

and subtracting means connected to the VI_(DWCP) signal means and to the J signal means and receiving direct voltage VI_(RP) for subtracting signal VI_(DWCP) from voltage VI_(RP) to provide the ΔVI signal to the J signal means.
 7. A system as described in claim 6 in which flow rate of the heavy sweet charge oil is controlled and the flow of the furfural is maintained at a constant rate and the control signal means receives signal SOLV from the flow rate sensing means, the J signal from the J signal means and a direct current voltage corresponding to a value of 100 and provides a signal C to the apparatus means corresponding to a new heavy sweet charge oil flow rate in accordance with the J signal, signal SOLV and the received voltage and the following equation:

    C=(SOLV)(100)/J

so as to cause the apparatus means to change the heavy sweet charge oil flow to the new flow rate.
 8. A system as described in claim 6 in which the controlled flow rate is the furfural flow rate and the flow of the heavy sweet charge oil is maintained constant, and the control signal means is connected to the sensing means, to the J signal means and receives a direct current voltage corresponding to the value of 100 for providing a signal SO corresponding to a new furfural flow rate in accordance with signal CHG and the J signal and the received voltage, and the following equation:

    SO=(CHG)(J)/100,

so as to cause the furfural flow to change to the new flow rate. 